Japanese Patent Application No. 11-273061 filed Sep. 27, 1999 is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of recording information in a phase-change recording medium comprising a phase-change material in a recording layer thereof, which phase-change material is capable of recording information in a rewritable manner and reproducing recorded information by being subjected to phase change at the irradiation with a laser beam. The present invention also relates to a phase-change recording medium produced by the method of recording information of the present invention, such as a rewritable compact disk (CD-RW), and other recording media for use in optical memory appliances.
2. Discussion of Background
As described in Japanese Laid-Open Patent Application 63-29336, there is conventionally known a method of recording information signals in an optical disk, using an optical disk recording apparatus, by causing a laser beam to scan the optical disk in such a manner that the surface of the optical disk is irradiated with a light spot of the laser beam, for instance, with the light spot of the laser beam being subjected to power modulation with information signals.
Furthermore, there is conventionally known a method of determining or setting optimum recording conditions such as recording (light) power, and the pulse width of recording (light) power by reproducing the information signals recorded in the optical disk and monitoring the reflection amplitudes of the reproduced signals or the length of a recording mark.
Various recording compensation methods have been disclosed for improving the quality of recording signals in the phase-change recording.
For example, in Japanese Laid-Open Patent Application 63-26632, as an effective method for improving the quality of recording signals, there is disclosed a method of recording long amorphous marks, using a pulse train in a PWM (pulse width modulation) method by use of a recording film with a high crystallization speed.
Furthermore, in Japanese Laid-Open Patent Application 63-266633 and U.S. Pat. No. 5,150,352, there is disclosed a method of controlling the fluctuations of the positions of the edge portions of a recording mark for marking an improvement in the reduction of the jitters by increasing the laser energy at the leading edge and the tail-end edge of a pulse train, or by lengthening laser irradiation time.
Orange Book Part III (ver 2.0) provides the standard of CD-RW for line recording at one to quadruple speeds (1.2 to 5.6 m/s). Such low line speeds take a long time for recording, so that there has been a demand for a rewritable compact disk capable of performing rewritable recording at higher speed.
Due to the above disclosed prior art, phase-change disks and optical disk drives having excellent performance have been made available. However, there has been desired further improvement on the technology for producing the optical disk and optical disk drive in order to obtain an optical disk which is securely compatible with CD-R(recordable), and an optical disk drive for use with the optical disk, which have completely satisfactory performance in overall aspects thereof, and which can create a new market of optical disk and optical disk drive.
By use of the conventional methods, however, it is extremely difficult to find most appropriate recording conditions without fail even if information signals are recorded in the conventional optical information recording media by a conventional, ass-produced optical information recording and reproducing apparatus for the following reasons:
In the above-mentioned conventional methods, there is known a method for determining a most appropriate recording power for each optical information recording and reproduction apparatus by monitoring the amplitudes of recording signals, that is, the difference between a signal level in an unrecorded portion and a signal level in a recorded portion of the recording medium, which amplitude constitutes a representative reproduction signal in the optical information recording medium.
However, it is known that the value of the amplitude of the recording signal is varied not only by the recording power, but also by the wavelength of the LD (laser diode) of the recording and reproduction apparatus, the numerical aperture of an optical pickup, the rim intensity (the intensity distribution of a laser beam which enters a condenser lens), the size or the shape of a light spot, and the pollution of the optical system with time, so that the optimum recording laser power and the quality of recorded signals are largely varied. Therefore, the conventional optical drives for the optical disk recording apparatus have been designed so as to be made compatible with different types of optical disks produced by different manufacturers thereof.
It is therefore a first object of the present invention to provide a method of recording information in a phase-change recording medium, which is free of the above-mentioned shortcomings of the conventional recording methods, and has the following features: The method includes a test recording step and is capable of attaining high recording performance without resort to a particularly selected combination of a rewritable compact disk and a compact disk drive, and also is capable of significantly improving the initial characteristics and overwrite characteristics of the rewritable compact disks and compact disk drives used therewith. The method is also suitable for performing recording and erasing of information, using a compact disk with a rotation speed in a wide range of 1.2 m/s to 22.4 m/s in terms of line speed.
A second object of the present invention is to provide a phase-change recording medium which is produced by the above-mentioned recording method.
The first object of the present invention can be achieved by a method of recording information in a phase-change recording medium comprising the steps of:
conducting a test recording with the application of a laser beam to the phase-change recording medium, the laser beam comprising a plurality of pulse trains, each pulse train comprising alternately (a) a comb-shaped pulse train portion and (b) a flat pulse-free portion, with a duty ratio of the comb-shaped pulse train portion being changed, thereby recording a plurality of signals in the recording medium,
reproducing the plurality of recorded signals, and
obtaining the relationship between the amplitudes of signals reproduced from the recorded signals and the duty ratios corresponding thereto in order to specify a pulse strategy for recording information in the phase-change recording medium.
More specifically, the first object of the present invention can be achieved by a method of recording information in a phase-change recording medium with a predetermined recording line speed, comprising the steps of:
conducting a test recording with the application of a laser beam to a predetermined portion of the phase-change recording medium, the laser beam comprising a plurality of pulse trains, each pulse train comprising alternately (a) a comb-shaped pulse train portion comprising a plurality of pairs of pulses, one with a pulse width T1 and a recording power P1, and the other with a pulse width T2 and a recording power P3, and (b) a flat pulse-free portion with a recording power P2, wherein P1, P2 and P3 are in the relationship of P1 greater than P2xe2x89xa7P3 in terms of the intensity of the light of the laser beam, and each of the comb-shaped pulse train portion and the flat pulse-free portion has the same duration width, with a duty ratio of the comb-shaped pulse train portion, defined by T1/(T1+T2) wherein 1/(T1+T2) is a clock frequency, being changed, thereby recording a plurality of signals in the recording medium,
reproducing the plurality of recorded signals to obtain reproduced signals corresponding to the plurality of recorded signals and to determine the amplitudes of the respective reproduced signals, and
obtaining the relationship between the amplitudes of the respective reproduced signals and the duty ratios corresponding thereto in order to specify a pulse strategy for recording information in the phase-change recording medium.
By use of the above-mentioned method, an appropriate recording pulse can be selectively set to such a degree of precision that is sufficient for use in practice, without optical information recording and reproducing apparatus, in particular, a mass-produced one, suffering any effects of the amplitude of a recording signal and a recording power offset, which effects are apt to become evident among such optical information recording and reproducing apparatus.
The above-mentioned method may further comprise the step of selectively designating (1) at least one amplitude with a magnitude of at least 80% of that of a maximum amplitude from the amplitudes of the respective reproduced signals and (2) the duty ratio corresponding thereto, whereby an appropriate pulse strategy for recording information can be specified efficiently, with higher precision, and the production costs for the optical information recording and reproducing apparatus for use with this method can be reduced.
The above-mentioned method can also include the step of recording as an information code in the phase-change recording medium the above-mentioned relationship between the amplitudes of the respective reproduced signals and the duty ratios corresponding thereto, or at least one of (1) at least one amplitude with a magnitude of at least 80% of that of a maximum amplitude from the amplitudes of the respective reproduced signals and (2) the duty ratio corresponding thereto, whereby the recording can be carried out without the test recording for each recording medium can be avoided, and exclusive tracks for the test recording can be eliminated the phase-change recording medium.
Furthermore, the above-mentioned method may further comprise the step of recording the recording power P1 in advance as an information code in the phase-change recording medium, whereby the mechanism of the optical information recording and reproducing apparatus for use with this method can be simplified, and the speed of the recording operation thereof can be increased.
The first object of the present invention can also be achieved by a method of recording information in a phase-change recording comprising the steps of:
conducting a test recording with the application of a laser beam to the phase-change recording medium, the laser beam comprising a comb-shaped pulse train, with a duty ratio of the comb-shaped pulse train being changed, thereby forming laser-beam applied portions in the recording medium,
applying light to the laser-beam applied portions to measure the intensities of the light reflected from the laser-beam applied portions, and
obtaining the relationship between the intensities of the light and the duty ratios corresponding thereto in order to specify a pulse strategy for recording information in the phase-change recording medium.
More specifically, the first object of the present invention can also be achieved by a method of recording information in a phase-change recording medium with a predetermined recording line speed, comprising the steps of:
conducting a test recording with the application of a laser beam to a predetermined portion of the phase-change recording medium, the laser beam comprising a comb-shaped pulse train which comprises a plurality of pairs of pulses, one with a pulse width T1 and a recording power P1, and the other with a pulse width T2 and a recording power P3, wherein P1 and P3 are in the relationship of P1 greater than P3 in terms of the intensity of the light of the laser beam, with a duty ratio of the comb-shaped pulse train, defined by T1/(T1+T2) wherein 1/(T1+T2) is a clock frequency, being changed, thereby forming laser-beam applied portions in the recording medium,
applying light to the laser-beam applied portions to measure the intensities of the light reflected from the laser-beam applied portions, and
obtaining the relationship between the intensities of the light and the duty ratios corresponding thereto in order to specify a pulse strategy for recording information in the phase-change recording medium.
The above-mentioned method may further comprise the step of selectively designating (1) at least one intensity of the light which is at least 80% of a maximum intensity of the light from the intensities of the light and (2) the duty ratio corresponding thereto.
The above-mentioned method can also include the step of recording as an information code in the phase-change recording medium the above-mentioned relationship between the intensities of the light and the duty ratios corresponding thereto, or at least one of (1) at least one intensity of the light which is at least 80% of a maximum intensity of the light from the intensities of the light and (2) the duty ratio corresponding thereto.
Furthermore, the above-mentioned method may further comprise the step of recording the recording power P1 in advance as an information code in the phase-change recording medium.
The first object of the present invention can also be achieved by the first mentioned method of recording information in a phase-change recording medium, with the addition of the steps of:
designating one duty ratio from the relationship between the amplitudes of the respective reproduced signals and the duty ratios corresponding thereto,
conducting a test recording with the application of a laser beam to a predetermined portion of the phase-change recording medium, the laser beam comprising a plurality of pulse trains, each pulse train comprising alternately (a) a comb-shaped pulse train portion comprising a plurality of pairs of pulses, one with a pulse width T1 and a recording power P4, and the other with a pulse width T2 and a recording power P6, and (b) a flat pulse-free portion with a recording power P5, wherein P4, P5 and P6 are in the relationship of P4 greater than P5xe2x89xa7P6 in terms of the intensity of the light of the laser beam, and each of the comb-shaped pulse train portion and the flat pulse-free portion has the same duration width, with the recording power P4 being changed, thereby recording a plurality of signals in the recording medium,
reproducing the plurality of recorded signals to obtain reproduced signals corresponding to the recorded signals and to determine the amplitudes of the respective reproduced signals, and
obtaining the relationship between the amplitudes of the respective reproduced signals and the recording powers P4 corresponding thereto in order to specify a pulse strategy for recording information in the phase-change recording medium, in which P4, P5 and P6 may be respectively the same as or different from P1, P2, and P3 in the first mentioned method.
The above-mentioned method may further comprise the step of selectively designating (1) at least one amplitude with a magnitude of at least 80% of that of a maximum amplitude from the amplitudes of the respective reproduced signals and (2) the recording powers P4 corresponding thereto.
Furthermore, the above-mentioned method may further comprise the step of recording as an information code in the phase-change recording medium the relationship between the amplitudes of the respective reproduced signals and the recording powers P4 corresponding thereto.
Furthermore, the above-mentioned method may further comprise the step of recording as an information code in the phase-change recording medium at least one of (1) at least one amplitude with a magnitude of at least 80% of that of a maximum amplitude from the amplitudes of the respective reproduced signals and (2) the recording power P4 corresponding thereto.
The second object of the present invention can be achieved by a phase-change recording medium produced by any of the above-mentioned methods for use in a method of recording information in an optical information recording medium with a predetermined recording line speed, wherein any of the above-mentioned information codes is recorded in advance in a predetermined portion of the phase-change recording medium.